Diffie-Hellman Key Exchange Overview Answers 1. What is the primary purpose of the Diffie-Hellman key exchange protocol? A. To directly transmit the secret key B. To replace symmetric encryption algorithms C. To allow two parties to securely agree on a secret key D. To encrypt messages using asymmetric encryption Answer: To allow two parties to securely agree on a secret key (C) The core idea of the Diffie-Hellman key exchange is to enable secure key agreement without directly transmitting the secret key. 2. Which of the following is NOT a necessary component of the Diffie-Hellman key exchange? A. A public primitive root B. A shared prime number C. Secret integers chosen by each party D. An established symmetric key Answer: An established symmetric key (D) The Diffie-Hellman key exchange requires a shared prime number, a public primitive root, and secret integers, but does not require an already established symmetric key. 3. How does Party A calculate the shared secret key in the DiffieHellman method? A. By multiplying the received public key by their private key and taking modulo p B. By using their own private key and intermediary public keys C. By directly summing both public keys D. By calculating the product of both private keys Answer: By multiplying the received public key by their private key and taking modulo p (A) Party A calculates the shared secret key by using Party B's public key and their own secret exponent. 4. What type of attacks can undermine the security of the DiffieHellman key exchange? A. Denial of service attacks B. Eavesdropping attacks C. Replay attacks D. Man-in-the-middle attacks Answer: Man-in-the-middle attacks (D) Man-in-the-middle attacks are a key vulnerability in the Diffie-Hellman protocol, allowing an attacker to intercept and manipulate key exchanges. 5. Which of the following choices explains a potential vulnerability related to parameter selection in the Diffie-Hellman key exchange? A. Utilizing complex primes ensures efficient calculation B. Using very small primes can make the exchange predictable C. Selecting large primes guarantees absolute security D. Choosing common values for g is always safe Answer: Using very small primes can make the exchange predictable (B) Weak parameter selection, such as using small primes, can be exploited by attackers, making the key exchange vulnerable. 6. In the context of Diffie-Hellman, what does the term 'primitive root modulo p' refer to? A. A generator that covers all possible values modulo p B. A variable placeholder in the algorithm C. The final computed shared key D. A random integer chosen for secure communication Answer: A generator that covers all possible values modulo p (A) A primitive root modulo p is a number such that powers of g, taken modulo p, cover all possible values, which is essential for the key exchange. 7. What is one of the main advantages of Elliptic Curve DiffieHellman (ECDH) compared to traditional Diffie-Hellman? A. It requires smaller key lengths for equivalent security B. It allows for larger keys to be used C. It is primarily for symmetric key exchange D. It eliminates the need for a public key Answer: It requires smaller key lengths for equivalent security (A) ECDH provides equivalent security with smaller key sizes, making it more efficient than traditional Diffie-Hellman. 8. What is the meaning of 'k' in the Diffie-Hellman key exchange process? A. The public key generated by Party A B. The shared prime number used in the exchange C. The shared secret key calculated by both parties D. The integer selected by Party B Answer: The shared secret key calculated by both parties (C) 'k' represents the shared secret key that both parties calculate independently after exchanging their public keys.